Automated systems exist for collecting data from meters that measure usage of resources, such as gas, water and electricity. Such systems may employ a number of different infrastructures for collecting this meter data from the meters. For example, some automated systems obtain data from the meters using a fixed wireless network that includes, for example, a central node in communication with a number of endpoint nodes (e.g. meter reading devices (MRDs) connected to meters). At the endpoint nodes, the wireless communications circuitry may be incorporated into the meters themselves, such that each endpoint node in the wireless network comprises a meter connected to an MRD that has wireless communication circuitry that enables the MRD to transmit the meter data of the meter to which it is connected.
One type of infrastructure, known in the art as Advanced Metering Infrastructure (AMI), uses two-way communications between collectors and single phase (SP) metering nodes and polyphase (PP) metering nodes to enable collection of metering data, such as kilowatt-hour (kWh), demand, interval, and time-of-use (TOU) data, as well as to enable control actions, such as disconnect, load management, or thermostat control. An AMI system typically consists of meter points connected to a collector via a local area network (LAN). The collector, in turn, is connected to a central head end system via a wide area network (WAN). Because these systems are typically deployed throughout a distribution grid at each point of service, it is desirable that such systems be economical for very large scale deployments. Another type of infrastructure is known in the art as Automatic Meter Reading (AMR). AMR and AMI systems are part of utility planning in the United States and many foreign countries. There are a large number of different communications systems concepts being offered for sale. Most of these concepts use the 900 MHz ISM frequency band and implement frequency hopping spread spectrum techniques. Because most of these systems are developed by communications experts rather than meter/utility systems experts, they can be highly complex and difficult to troubleshoot.
Some networks may employ a mesh networking architecture. In such networks, known as “mesh networks,” endpoint nodes are connected to one another through wireless communication links such that each endpoint node has a wireless communication path to the central node. One characteristic of mesh networks is that the component nodes can all connect to one another via one or more “hops.” Due to this characteristic, mesh networks can continue to operate even if a node or a connection breaks down.
In a mesh network, some endpoint nodes may transmit their meter data directly to the central node. These endpoint nodes are known as “level 1” nodes because a data communication only needs to complete one “hop” to travel from the endpoint node to the central node or vice versa. Other endpoint nodes may transmit their meter data to the central node indirectly through one or more intermediate bidirectional nodes that serve as repeaters for the meter data of the transmitting node. For example, a “level 2” node transmits its meter data to the central node through one bidirectional node, while a “level 5” node transmits its meter data through four bidirectional nodes.
FIG. 4 illustrates an example metering system having a wireless mesh network architecture. As shown, a central node, such as a collector 116, collects and stores data from a number of meters (i.e., nodes). Bidirectional nodes 114a-114k may include bidirectional transmitting and receiving devices each with a wireless communication path to the collector 116 that is either a direct path or an indirect path through one or more intermediate bidirectional nodes serving as relay nodes. For example, bidirectional nodes 114a and 114b have direct communications paths to the collector 116, while bi-directional nodes 114c-114k have indirect communications paths to the collector 116 through one or more intermediate nodes. In some networks (such as the exemplary network shown in FIG. 1), each bidirectional node 114a-114k has a single, designated path to the central node 116, while, in other networks, multiple dynamic paths may exist between each bidirectional node and the central node. In networks where each bidirectional node 114a-114k has only a single, designated path to the central node 116, only those nodes along the designated path will relay a message from the node with that designated path. In other networks, multiple bidirectional nodes may relay, or retransmit, a message from a given node.
So-called “one-way” or “transmit-only” nodes 451-456 may include transmit-only meters such as water or gas meters. The transmit-only nodes 451-456 may gather and transmit meter data that is then relayed by one or more bidirectional nodes 114a-114k to the collector 116. The system depends on the transmissions from a transmit-only device being received by at least one bidirectional node and then relayed through the network to the collector 116. Each bidirectional node may be within range and capable of receiving meter data directly from multiple transmit-only nodes. For example, bidirectional node 228 is capable of receiving meter data directly from transmit-only nodes 252-254. Consequently, the meter data transmitted by a given transmit-only node may be received by multiple bi-directional nodes and thus relayed through the network to the central node multiple times.
A variety of mesh architectures are used to read electric, gas, and water meters. Many systems using mesh architectures can perform “on demand” reads from the collector, but the normal mode of operation is for endpoints to “bubble up” data to the collector. Because the collector is the receiver for all of these data communications, the area around the collector will have the highest communication traffic of any place within the mesh network. In order to eliminate contention between data communications within bubble up mesh networks, sophisticated synchronization schemes are typically used to ensure that both frequency and time are kept extremely accurately. It is important for endpoints to maintain synchronization to know when to transmit data and on what frequency to transmit data. If synchronization is lost, the throughput of the system can be adversely affected.
Thus, a need continues to exist for a more efficient mechanism for managing multiple communications within a mesh network.